This invention concerns a method and apparatus for modulating the flow and pressure of a fluid passing through a container and in particular through a combustor assembly.
A gas turbine engine typically comprises in flow series order a compressor, a combustor and a turbine. Air entering the compressor is compressed before fuel is added and in the combustor and ignited. The resultant hot gasses pass to the turbine where they are expanded to produce work that is used to power the compressor and additionally to provide thrust, further work or electrical power.
The combustion process can create thermoacoustic instabilities within the combustor that can interact with the combustion process to provide areas of poor combustion, exaggerated acoustic waves that could damage the combustor and noise such as, for example, rumble.
It is desirable to model the interaction of the acoustic wave field with the combustion process in order to understand the unsteady characteristics of the combustion process. Once the characteristics are understood it becomes possible to address and potentially absorb damage and noise problems.
In a known rig a series of forced, but controlled wave-fields are imposed onto the burners in a combustor arrangement by a siren. The siren has a first rotating parallel plate and a second static parallel plate spaced axially from the first plate. The first plate rotates about an axis that is generally parallel with the combustor axis. Each plate has a series of holes that periodically align to create an unsteady flow and acoustic waves.
Since the combustor produces high temperatures it is necessary to position the siren upstream of the combustion chamber to prevent significant damage. The siren presents a large surface area which is difficult to cool and is easily damaged by combustion gasses. The siren can not be acceptably applied to the high pressures and high air mass flow rates within the combustor during operation and is limited to within laboratories at much lower pressures and temperatures than typically observed in the industrial use of a gas turbine engine. Clearly this leads to incorrect modelling of the acoustic process.